Neon Tetras Have White Growth On Its Nose

[leebo]

hi i,m pretty new to keeping fish but i have 2 neon tetras with a white growth on their nose,its like a semi circle ,i have a 45 gallon tank with 3 guppies,6 zebra danios ,10 neon tetras,2 angel fish ,1 upside down catfish,4 penguin tetras and a red tailed black shark.i've had the tank for 7 months
and had a couple of fish die but not for about 2 months, amonia : 0,nitrate : 25, nitrite : 0, GH : 125 , KH :50/100, PH :7.2 these numbers ha been the same for the last 2 months,
 

 

[Byron]

Can you post a photo of the neon(s)?
 
I would aim to get your nitrate lower, 20 ppm is the max it should be, and preferably lower.  Regular (every week) water changes of half the tank volume should help achieve this.  Live plants would too.
 
You have a lot of fish for a 45 gallon tank, when you consider the mature size of some of them.  The Red Tailed Black Shark will really outgrow this space, and this fish can sometimes turn quite nasty.
 
Byron.

 

[DoubleDutch]

This problem is quite common with neons (and cardinals) in the last few months. It doesn't seem to be treatable (not very contagious or lethal as well btw), so my thoughts go to a viral infection like lympfocystis.
Have seen threads in several countries and continents about this,